The present invention relates to a vertebral implant. More particularly this invention concerns such an implant used to replace one or vertebrae and/or intervertebral disk.
When a vertebra is broken or crushed it is frequently necessary to ablate the body of the crushed or broken vertebra or vertebra as well as any damaged intervertebral disk. In order, however, to prevent the spinal column from collapsing with damage to the fragile spinal cord running in the vertebral foramen forward of the vertebral body, it is necessary to implant a spacer. This implant is braced vertically between the bodies of the adjacent vertebra and holds them apart at the desired spacing.
In commonly owned U.S. Pat. No. 5,571,192 a spinal implant is described having a tubular center part extending along an axis and a pair of end parts. The center part is formed with upper and lower screwthreads of opposite hand and with a plurality of radially throughgoing apertures. The upper and lower tubular end parts are each formed with a plurality of radially throughgoing apertures, each have a circular-section inner end threaded onto a respective one of the screwthreads, and each have an outer end adapted to bear on a respective one of the adjacent vertebrae.
Such an implant is highly effective. Nonetheless its installation is somewhat tricky until it has been expanded into place so that the two end parts bite into the respective vertebrae. In addition the entire implant area is not stable until there has been substantial bone growth around and through the implant, so that the patient must be very careful to avoid any displacement of the implant before it sets fully.
It is therefore an object of the present invention to provide an improved vertebral implant.
Another object is the provision of such an improved vertebral implant which overcomes the above-given disadvantages, that is which can be solidly anchored in place.
A spinal implant for engagement in a space between a pair of adjacent vertebrae has according to the invention a center part extending along an axis and formed with upper and lower screwthreads of opposite hand. Respective upper and lower end parts axially flank the center part and each have an inner end threaded onto a respective one of the screwthreads and an outer end adapted to bear on a respective one of the adjacent vertebrae. One of the end parts is formed with an eye having a hole open transversely of the axis. A screw engages through the hole and anchors the one end part to the respective vertebra. Normally in accordance with the invention the other of the end parts is also formed with an eye having a hole open transversely of the axis and another screw engages through the hole of the other end part and anchors the other end part to the respective vertebra.
Thus it is possible to anchor the implant solidly to the spine. The cortical screws engage well into the respective vertebrae so that the implant is not only held in place by engagement of upper and lower normally toothed faces of the end parts in the overlying and underlying vertebrae, but also by these screws. The result is a solid uniting of the implant to the two flanking vertebrae. Thus even if considerable torque is exerted on the center part to distract these vertebrae, the end parts will stay put.
The ability to anchor both end parts to the respective vertebrae is particularly advantageous when accommodating certain installations. For example when the implant is to be installed at the lower end of the vertebrae above the sacral vertebrae, it is advantageous to be able to work from above, with screws angled down through the lower element into the sacrum. Thus the operating field can be small. Furthermore the implant lies wholly between the vertebrae it is mounted between, within the vertical projection of the spine so that it can be left in place and the operating wound can be closed and left closed.
The eye of the other end part according to the invention is formed as a tab extending generally parallel to the axis so that its hole and the screw through it is generally perpendicular to the axis.
In another arrangement the eye is open at an acute angle away from the other part and is thickened. Normally the eye is open at an angle of between 25xc2x0 and 65xc2x0 to the axis, preferably 45xc2x0.
The eye according to the invention is unitarily formed with the one end part. In addition the inner ends are formed as axially extending stems and the center part is a sleeve threaded over the stems. In addition the parts are formed with radially open throughgoing holes so that bone can grow into and through the parts. These parts can be made of titanium, a biocompatible plastic, ceramic, or bone.